Sean, also spelled Seán or Séan in Hiberno-English, is a male given name of Irish origin. It comes from the Irish versions of the Biblical Hebrew name Yohanan (יוֹחָנָן), Seán (anglicized as Shaun/Shawn/Shon) and Séan (Ulster variant; anglicized Shane/Shayne), rendered John in English and Johannes/Johann/Johan in other Germanic languages. The Norman French Jehan (see Jean) is another version. In the Irish language, the presence and placement of the síneadh fada is significant, as it changes the meaning of the name. The word "Sean" in Irish means "old", while the word "Séan" means "omen".
https://en.wikipedia.org/wiki/Sean